--- title: "Operation of pumped storage hydro plant" subject: "Power Plant Equipment" chapter: 1 key: "semester_7/power_plant_equipment:pump-storage-operation" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/pump-storage-operation site: BCT Engineering --- # Operation of pumped storage hydro plant Power Plant Equipment · Chapter 1: Hydro Power Plant - Asked in: 2076 Asoj, 8 marks; 2072 Chaitra, 4 marks (asked 2 times) - Video: [Hydropower Explained Inside a Pumped Storage Power Plant | How It Works](https://www.youtube.com/watch?v=E-m7Psbuup0) — saVRee - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/pump-storage-operation - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-1 ## Question Explain the operation of pump storage type hydro power plant with neat diagram. ## Short answer A pumped storage plant has two reservoirs at different levels. During off-peak, surplus electricity pumps water from the lower to the upper reservoir. During peak demand, water is released back through a turbine-generator to produce power. It functions as a large rechargeable battery for the grid. ## Answer A **pumped storage plant** is a hydro plant with two reservoirs at different levels. It uses cheap surplus electricity in off-peak hours to pump water from the lower reservoir to the upper one, and releases the same water back through the turbine to generate power during peak hours. It works like a large rechargeable battery for the grid. ```text UPPER RESERVOIR (head pond) ~~~~~~~~~~~~~~~~~~~~~~~ | penstock / pressure shaft | (water flows down when | generating, up when pumping) v ^ +---------------------+ +-----------+ | reversible |------| motor- |---- grid | pump-turbine | | generator | (supply +---------------------+ +-----------+ or draw) | ^ v | tailrace ~~~~~~~~~~~~~~~~~~~~~~~ LOWER RESERVOIR (tail pond) ``` **Main parts:** upper reservoir, lower reservoir (or river/tail pond), intake, penstock or pressure shaft, power house with a reversible pump-turbine (usually Francis type) coupled to a reversible synchronous motor-generator, and tailrace. **Operation:** 1. **Generating mode (peak hours):** Water from the upper reservoir flows down the penstock, drives the machine as a turbine, and the machine works as a generator feeding the grid. The water is collected in the lower reservoir. 2. **Pumping mode (off-peak hours, e.g. night):** Surplus power from base-load plants (thermal, nuclear or run-of-river hydro) drives the machine as a motor. The machine rotates in the reverse direction and works as a pump, lifting water from the lower reservoir back to the upper reservoir. 3. The cycle repeats daily (or weekly/seasonally). **Energy relation:** Energy stored $E = \rho g V H$. Overall cycle efficiency $$ \eta_{cycle} = \frac{E_{generated}}{E_{pumping}} \approx 0.70 \text{ to } 0.80 $$ So about 1.3 kWh of off-peak energy is used to get 1 kWh at peak. It is still economic because peak energy is far more valuable than off-peak energy. **Advantages:** - Supplies peak load quickly (start-up in a few minutes); also gives spinning reserve and frequency support. - Lets base-load thermal plants run at a steady, efficient load; raises the system load factor. - Very little water is consumed; the same water is used again and again. - Long life and low running cost. **Limitations:** high capital cost, need for suitable topography with two reservoir sites, and a net energy loss of 20–30 %. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which machine set is typically used in a pumped storage power house? A. Separate Pelton turbine and a diesel pump B. Reversible Francis pump-turbine with reversible synchronous motor-generator C. Kaplan turbine with an induction generator only D. Steam turbine with a boiler feed pump Answer: B. A reversible pump-turbine coupled to a motor-generator works as turbine/generator or pump/motor. (Key point: Plant arrangement) 2. In pumping mode, what supplies the power and what happens to the machine? A. Surplus power from base-load plants drives it as a motor in reverse rotation, lifting water to the upper reservoir B. Peak-hour power drives it as a generator C. The upper reservoir water drives it as a turbine D. It stays at rest while another pump lifts water Answer: A. Off-peak surplus drives the machine as a motor rotating in reverse, working as a pump. (Key point: Pumping mode) 3. Which statement about energy in a pumped storage plant is correct? A. It produces more energy than it consumes B. It is a net consumer of energy, with 20-30 % cycle loss C. Its cycle efficiency is about 100 % D. It consumes a lot of water each cycle Answer: B. Overall cycle efficiency is 70-80 %, so it uses more off-peak energy than it returns, but the same water is reused. (Key point: Energy and efficiency) 4. Which is an advantage of pumped storage? A. Very low capital cost B. Works on flat terrain without two reservoirs C. Consumes large amounts of water D. Starts in minutes, supplies peak load and spinning reserve, and lets thermal plants run steadily Answer: D. Fast start, reserve and load-factor improvement are its main advantages; high cost and site needs are limitations. (Key point: Advantages) ## Related in Power Plant Equipment - [Pumped storage plant and feasibility in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-nepal-feasibility) — Power Plant Equipment, chapter 1, asked 5× - [Francis turbine in pumped storage plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Afrancis-turbine-pumped-storage) — Power Plant Equipment, chapter 1 - [Pumped storage to reduce peak generation loss](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-peak-loss) — Power Plant Equipment, chapter 1, asked 3× - [When pumped storage is economically feasible](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apumped-storage-economic-feasibility) — Power Plant Equipment, chapter 1 - [Function of surge tank in hydro plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asurge-tank-function) — Power Plant Equipment, chapter 1 - [Steady state operation of hydropower plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Ahydropower-steady-state-operation) — Power Plant Equipment, chapter 1 ## Related in other subjects - [Pumped storage plant: power, turbine, setting, surge](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-turbine-surge-numerical) — Hydropower Engineering, chapter 7 - [Pumped storage plant and benefit to Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-benefit-nepal) — Hydropower Engineering, chapter 2 - [Importance of storage plants; pumped storage layout](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Astorage-importance-pump-storage-layout) — Hydropower Engineering, chapter 2 - [Short note: Pumped storage hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apumped-storage-hydropower) — Energy Environment and Society, chapter 5